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      <h1 class="post-title">IOS中 new 和 alloc]init 等</h1>

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        <span class="post-time"> 2016-05-20 </span>
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            <a href="/categories/ios/"> iOS </a>
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          <span class="more-meta"> 约 383 字 </span>
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<h4 id="classname-new和classname-allocinit"><code>[className new]</code>和<code>[[className alloc]init]</code></h4>
<hr>
<ol>
<li>在实际开发中可能很少用到 <code>new</code> ，一般创建对象咱们看到的都是<code>[[className alloc]init]</code>,但是并不是意味着就不会接触到 <code>new</code> ,在一些代码中还是会看到使用 <code>new</code> ,还有面试的时候,也有可能会被问到.</li>
<li>那么,它们之间到底有什么不同呢?</li>
</ol>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
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<td class="lntd">
<pre tabindex="0" class="chroma"><code class="language-objective-c" data-lang="objective-c"><span class="line"><span class="cl"><span class="p">+</span> <span class="nf">new</span> 
</span></span><span class="line"><span class="cl"><span class="p">{</span> 
</span></span><span class="line"><span class="cl"><span class="kt">id</span> <span class="n">newObject</span> <span class="o">=</span> <span class="p">(</span><span class="o">*</span><span class="n">_alloc</span><span class="p">)((</span><span class="kt">Class</span><span class="p">)</span><span class="nb">self</span><span class="p">,</span> <span class="mi">0</span><span class="p">);</span> 
</span></span><span class="line"><span class="cl"><span class="kt">Class</span> <span class="n">metaClass</span> <span class="o">=</span> <span class="nb">self</span><span class="o">-&gt;</span><span class="n">isa</span><span class="p">;</span> 
</span></span><span class="line"><span class="cl"><span class="k">if</span> <span class="p">(</span><span class="n">class_getVersion</span><span class="p">(</span><span class="n">metaClass</span><span class="p">)</span> <span class="o">&gt;</span> <span class="mi">1</span><span class="p">)</span> 
</span></span><span class="line"><span class="cl"><span class="k">return</span> <span class="p">[</span><span class="n">newObject</span> <span class="n">init</span><span class="p">];</span> 
</span></span><span class="line"><span class="cl"><span class="k">else</span> 
</span></span><span class="line"><span class="cl"><span class="k">return</span> <span class="n">newObject</span><span class="p">;</span> 
</span></span><span class="line"><span class="cl"><span class="p">}</span> 
</span></span><span class="line"><span class="cl"> 
</span></span><span class="line"><span class="cl"><span class="c1">//而 alloc/init 像这样： 
</span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="p">+</span> <span class="nf">alloc</span> 
</span></span><span class="line"><span class="cl"><span class="p">{</span> 
</span></span><span class="line"><span class="cl"><span class="k">return</span> <span class="p">(</span><span class="o">*</span><span class="n">_zoneAlloc</span><span class="p">)((</span><span class="kt">Class</span><span class="p">)</span><span class="nb">self</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">malloc_default_zone</span><span class="p">());</span>  
</span></span><span class="line"><span class="cl"><span class="p">}</span> 
</span></span><span class="line"><span class="cl"><span class="p">-</span> <span class="nf">init</span> 
</span></span><span class="line"><span class="cl"><span class="p">{</span> 
</span></span><span class="line"><span class="cl"><span class="k">return</span> <span class="nb">self</span><span class="p">;</span> 
</span></span><span class="line"><span class="cl"><span class="p">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>通过源代码中我们可以发现<code>[className new]</code>基本等同于<code>[[className alloc] init]</code>;区别只在于 alloc 分配内存的时候使用了 zone 。这个 zone 是什么东东呢？它是给对象分配内存的时候。把关联的对象分配到一个相邻的内存区域内，以便于使用时消耗很少的代价，提升程序处理速度；
3. 为什么不推荐使用 new 呢？
如果，使用 new 初始化方法被固定为 init，而你又想使用 initWithXXX 怎么办？没办法！</p>
<blockquote>
<p>未完待续。。。</p>
</blockquote>

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